“…3b, the characteristic peak of C O C group on the POA400-DGEBA was strongly observed at 1105 cm −1 [50,51]. Moreover, the peak of the secondary amine (C NH C) appears significantly at 1204 cm −1 , implying the POA400-DGEBA have been effectively synthesized via the reaction of DGEBA epoxy and POA400 [50,51]. As expected, the peak observed at 1460 cm −1 corresponds to the CNH stretching and the peak at 1630 cm −1 was detected for the stretching vibration of the C O group, respectively, due to the formation of amide linkages [52,53].…”